Catalytic oxidation of olefins to yield carboxylic acids

ABSTRACT

Olefins are oxidized with a mineral acid to carboxylic acids by dissolving the olefin in a hydrophobic solvent, and contacting the olefin solution with an oxidation system which comprises a mineral acid, an aqueous solution of a hexavalent chromium compound and a ruthenium compound. The reaction mixture is heated to a temperature of from about 45* C to about 100* C.

United States Patent Washecheck [is] 3,692,810 1 Sept. 19, 1972CATALYTIC OXIDATION OF OLEFINS T0 YIELD CARBOXYLIC ACIDS Paul H.Washecheck, Ponca City, Okla.

Assignee: Continental Oil Company, Ponca City, Okla.

Filed: Feb. 22, 1971 Appl. No.: 117,794

Inventor:

US. Cl. ..260/4l3, 260/533 R Int. Cl .Q ..C07c 51/32 Field of Search..260/533 R, 413

References Cited UNITED STATES PATENTS ll/l968 Keblys et al ..260/533 RX 3,076,032 l/ 1963 Riemenschneider et al. ...260/

Primary ExaminerLorraine A, Weinberger Assistant Examiner-Richard D.Kelly Attorney-Joseph C. Kotarski, Henry H. Huth, Robert B. Coleman, Jr.and Gerald L. Floyd and contacting the olefin solution with an oxidationsystem which comprises a mineral acid, an aqueous solution of ahexavalent chromium compound and a ruthenium compound. The reactionmixture is heated to a temperature of from about 45 C to about 100 C.

11 Claims, No Drawings CATALYTIC OXIDATION OF OLEFINS TO YIELDCARBOXYLIC ACIDS BACKGROUND OF THE INVENTION oxidizing olefins.

2. Brief Description of the Prior Art It has been proposed to oxidizeolefins to aldehydes and/or carboxylic acids using periodic acid in thepresence of ruthenium. The iodine yielded in the reac-' tion is,however, an expensive chemical and must be recovered substantiallyquantitatively in order to render the process economically attractive.Thisis difficult due to the high vapor pressure of iodine, itssolubility in organic solvents and its reactivity with many organiccompounds.

'Another method previously disclosed (in U. S. Pat. No. 3,076,032) foroxidizing olefins to carbonyl compounds is that of contacting theolefins with an acid, such as a mineral acid, a compound of one of thenoble metals belonging to group VIII of the periodic table, and a redoxsystem which includes an inorganic salt of a metal showing severalvalence states under the reaction conditions, such as chromium. Thecontact is carried out in an aqueous or hydrophilic solvent environment,and in the presence of a quinone compound. The group VIII noble metalsare reported to function as equivalents in the oxidation reaction, bothwith respect to the aldehyde and ketone products yielded, and withrespect to their susceptibility to regeneration by a number of describedredox systems, one of which, besides the chromium or compoundspreviously men tioned, is an Fe O redox system.

SUMMARY OF THE PRESENT INVENTION The present invention proposes the useof a new catalyst system for oxidizing olefins, and a new method,employing such catalytic oxidation, for producing. good yields ofcarboxylic acids. The method of the present invention departs from theprior art in its discernment of a difference in the catalytic effect ofa particular group VIII metal, ruthenium, in the oxidation of olefins,as compared to other group VIII metals,'such as palladium and osmium.Moreover, it has been determined that the redox system in which theruthenium may be included for purposes of regeneration during thoxidation of olefins is not as comprehensive as for some other groupVIII metals, such as palladium. Thus, hexavalent chromium functions wellas a regenerative oxidant for ruthenium, wherens ferric iron systems areineffective. Finally, though such group Vlll metalsas prises an aqueoussolution of a hexavalent chromium 2 compound, a mineral acid and aruthenium compound- The reaction mixture is heated to a temperature offrom about 45 C to about C, andpreferably to the reflux temperature ofthe hydrophobic solvent in which the olefin is dissolved.

An object of the invention is to provide a new method for preparingcarboxylic acids.

Another object of the invention isto provide a catalyst system forselectively oxidizing olefins to carboxylic acids.

A further object of the invention is to providea method forcatalytically oxidizing olefins so that the more expensive elements ofthe catalyst can be recovered or re-utilized in a relatively economicalmanner.

Other objects and advantages of the invention will become apparent asthe following detailed description of. the invention is read.

DETAILED DESCRIPTION OF THE INVENTION The olefins oxidized by contactwith the oxidation system used in the process of the invention may be 1-olefins or internal olefins, and may be cyclic or acyclic (straight orbranched chain). The olefin is dissolved in a hydrophobic solvent whichis substantially immiscible with water. Solvents which may be usedinclude, for example, paraffin hydrocarbons, both halogenated andnon-halogenated, ketones, benzene and toluene. Many others might bementioned, but will be known or easily ascertainable by those possessingchemical expertise.

The oxidation system with which the olefin solution is contactedconsists essentially of a ruthenium compound, a mineral acid and anaqueous solution of a compound of hexavalent chromium. The ruthenium maybe present in a number of forms, such as, for example, the metal,ruthenium dioxide, ruthenium tetroxide or a ruthenium halide salt. Onlya relatively small amount of ruthenium need be utilized in the catalystsystem. In general, from about 0.001 mole to about 0.01 mole ofruthenium is utilized per mole of the olefin subjected to oxidation. Theuse of from about 0.004 mole to about 0.008 mole of ruthenium ispreferred.

The mineral acid used in the oxidation system may be substantially anymineral acid. Typical useful mineral acids include nitric acid,hydrochloric'acid, sulphuric acid, perchloric acid, and phosphoric acid.The amount of mineral acid employed is not critical and may vary widely.The strength of the mineral acid may also vary over a considerablerange, but is preferably from about 2 molar to about 8 molar.

The form in which hexavalent chromium is present is not critical,provided it is present in aqueous solution. Although an aqueous solutionof chromium trioxidc may be very conveniently utilized, aqueoussolutions of other chromium salts may also be used, or the hexavalentchromium ions may be electrolytically regenerated in the course of theoxidation reaction. The amount of chromium utilized may vary from about1 mole to about 50 moles per mole of olefin subjected to oxidation, andan amount of about 10 moles of the chromium per mole of olefin ispreferred.

In the process of the invention, the ruthenium functions to oxidize theolefin starting material to the corr esponding carboxylic acidsaccording to the reaction 1n oxidizing the olefin, the rutheniumundergoes reduction from a higher to a lower valence state, and is thenregeneratively oxidized by the hexavalent chromium. Hexavalent chromiumis itself capable of oxidizing olefins at a slow rate to provide a lowyield of impure carboxylic acids contaminated with epoxides and otherby-products, and to avoid this undesirable oxidative efl0 fect of thechromium, the olefin is dissolved in a hydrophobic solvent (in which thechromium is substantially insoluble), and the chromium compound isdissolved in an aqueous or hydrophilic solvent.

The mineral acid utilized functions to contribute anions to the reactionenvironment to form salts on solution of chromium trioxide.

The oxidation reaction is carried out at a temperature of from about 40C to about 100 C, with operation at the reflux temperature of theparticular reaction system in use being preferred.

The following example will serve to illustrate typical oxidationreactions carried out in accordance with the process of the invention. Anumber of oxidation runs were carried out in a three-necked flaskequipped with a blade stirrer, a thermometer and a condenser. In eachreaction run, 500 ml of an aqueous mineral acid solution (type andconcentration varied between runs) and 50 grams (0.50 mole) of chromiumtrioxide was placed in the flask. The amount of ruthenium dioxide to be30 used as catalyst was then placed in the flask. A n-heptane solutionof 11.22 grams (0.10 mole) of l-octene was next added to the flask. Thereaction mixture was then heated to gentle reflux at 82 C.

In each run, the reaction mixture was sampled periodically and analyzedby gas chromatography. The concentration of each component wascalculated from a standard solution using the heptane solvent as aninternal standard. The results reported in Table 1 are the analyses ofthe last samples before the reaction was stoppedin each run.

ruthenium compounds, and a mineral acid, said contact being carried outat a temperature of from about C to about 100 C.

2. The method defined in claim 1 whereinsaid contact is carried out atthe reflux temperature of the reaction mixture.

3. The method defined in claim 1 wherein the amount of ruthenium in saidoxidation system is from about 0.001 mole to about 0.01 mole per mole ofthe olefin with which the oxidation system is contacted.

4. The method defined in claim 1 wherein said mineral acid is selectedfrom the group consisting of sulfuric acid, nitric acid, and perchloricacid.

5. The method defined in claim 1 wherein the amount of hexavalentchromium in said oxidation system is from about 1 mole to about molesper mole of the olefin with which the oxidation system is contacted.

6. The method defined in claim 1 wherein said hydrophobic solvent is anorganic liquid which is immiscible with water.

7. The method defined in claim 5 wherein said hexavalent chromiumcompound is chromium trioxide and said catalytic material is rutheniumdioxide.

8. The method defined in claim 7 wherein the amount of ruthenium in saidoxidation system is from about 0.001 mole to about 0.01 mole per mole ofthe olefin with which the oxidation system is contacted.

TABLE 1 Moles 01 mini-ml ncid 1-octonc, lcrccnt selectivity acids R1103,Reaction pcl'ccnt Percent; Run N0 1noles 10 11:80; 11010.1 llNOn timc,his. conversion Cu C7 Total yield 120 31). 4 1. 7 42. 7 43. 4 17. 1 4.024 .16. 5 6. U 83. 0 88. 0 84. 9 48 85. 7 10. 3 71. 0 82. 2 70. 4 4.0 4100.0 14.2 71. 7 85.0 85.1! 8. (l 2 U8. .5 14.8 75.1 89 1) 88. 4 .34 40.5 3. .2 7. 3 10 5 5. 2 4.1) 1 07. 6 14. 2 43. 0 57. 2 55. 8 4. l) 24111i. 5 5. (i 83. (J 88. 0 84.1] 4.0 4 100. 0 14. 2 71. 7 85. 0 85. J4.1) 1 .17. ii 14. 2 43. 0 57. 2 55. 8 4. 0 48 73. 8 8. 4 79. 1 87. 564. (i 4. 0 8 100. 0 13. S 64. 4 78. 2 78. 2 4. 0 1 85.11 14. 7 34. 849. 5 2. 5 4. 0 4H 85. 0 5. 9 75. 5 81. 4 (59. 2 4. 0 ti 08. 4 7. 8 78.5 86. 3 84. J

" Octenc conversion=1-octcnc consnmctl/l-octcno charged.

'* Percent sclcctivity=wcight 01' acid prorluccd/(thcorcticnl wciglit o1ucirl possiblc) (conversion).

c Pcrccnt yicld=pcrccnt conversion tiincs pcrccnt sclcctlvity.

From the foregoing description of the invention, it will be apparentthat a process of realizing high yields of carboxylic acids fromolefinic starting materials has been proposed. Although certainpreferred reaction conditions and typical reactants have been describedfor the purpose of illustrating the basic principles of the invention,it will be understood that changes in such conditions, and equivalentsof the reactants, may be

2. The method defined in claim 1 wherein said contact is carried out atthe reflux temperature of the reaction mixture.
 3. The method defined inclaim 1 wherein the amount of ruthenium in said oxidation system is fromabout 0.001 mole to about 0.01 mole per mole of the olefin with whichthe oxidation system is contacted.
 4. The method defined in claim 1wherein said mineral acid is selected from the group consisting ofsulfuric acid, nitric acid, and perchloric acid.
 5. The method definedin claim 1 wherein the amount of hexavalent chromium in said oxidationsystem is from about 1 mole to about 50 moles per mole of the olefinwith which the oxidation system is contacted.
 6. The method defined inclaim 1 wherein said hydrophobic solvent is an organic liquid which isimmiscible with water.
 7. The method defined in claim 5 wherein saidhexavalent chromium compound is chromium trioxide and said catalyticmaterial is ruthenium dioxide.
 8. The method defined in claim 7 whereinthe amount of ruthenium in said oxidation system is from about 0.001mole to about 0.01 mole per mole of the olefin with which the oxidationsystem is contacted.
 9. The method defined in claim 8 wherein the olefinis a 1-olefin.
 10. The method defined in claim 9 wherein saidhydrophobic solvent is an organic compound which is immiscible withwater.
 11. The methOd defined in claim 10 wherein said mineral acid isselected from the group consisting of sulfuric acid, nitric acid, andperchloric acid.